It is well known to use drilling fluids in earth drilling operations, for example in the mining and oil well drilling industries. These fluids provide cooling and lubricating properties and assist in the removal of the drilled material. A primary disadvantage associated with the use of drilling fluids is their expense, especially in the well drilling area where large volumes of fluid are required. In view of the high cost of drilling fluids, it is very desirable to develop ways of removing drilled particulate material suspended therein as a result of the drilling operations so that the fluids can be reused.
Attempts have been made in the past to develop effective ways of removing particulate material in drilling fluids resulting from drilling operations. The most common technique has been to introduce the drilling fluids containing particulate material into mud pits or settlement tanks which permits the material to settle out from the fluids. The clarified fluids are then drawn off at the top of the pit or tank, and are recirculated in the drilling operations. The major disadvantage associated with this technique is the length of time required for the material to settle out. A further disadvantage is that as the difference between the density of the material and the density of the fluid decreases, the length of time required for complete settling increases and, in many cases, complete separation of the material from the fluid cannot be achieved within a reasonable amount of time.
Certain devices have been suggested in the past for separating solid materials from fluids. U.S. Pat. No. 3,768,657 to Hoag relates to a device primarily for use in separating small metal cuttings from oil-based metal working coolants of the type generally used in machining operations. The device comprises a settling tank having one bottom wall inclined at an angle away from the bottom of the tank. The tank is also provided with a screen and a conveyor system having transverse members for removing settled material from the tank. The screen during normal operation of the device leans under its own weight against the conveyor system at an angle toward the inclined wall of the tank, so that the transverse members scrape the screen to dislodge cuttings trapped therein. The screen is pivotally mounted on the bottom of the tank so that if any material is firmly lodged in the screen, and is not removed by the transverse members, the screen is free to move away from the conveyor to permit the conveyor to continue its movement without any damage resulting to the transverse members. Fluids enter the device at a point near the inclined wall and flow in a substantially horizontal direction across the tank and through the screen to give a clarified fluid which is recovered from the tank. The Hoag device suffers from several disadvantages, the main one being that the screen is very easily blocked with material. This makes the device totally unsuited for use with earth drilling fluids containing large chunks of agglomerated material, especially in situations where the fluid has a thick mud-like consistency. When used with such fluids, the screen tends to become blocked with earth and sludge very rapidly after start up so that the amount of fluid passing through the screen is reduced to a minimum and overflow of fluid from the tank eventually occurs.
U.S. Pat. No. 3,674,145 to Schmutzler describes another type of device for clarifying fluids containing small particles of dust, said and the like. The device differs from the Hoag device in that it is not provided with a screen and separation is achieved entirely by settling out of the material. The device comprises a tank divided longitudinally into two compartments each containing baffles and a conveyor system. The end wall of the tank is inclined at an angle away from the bottom, and the baffles in each compartment are either substantially vertical to the bottom or inclined at an angle toward the inclined wall. Fluid containing suspended particulate material is passed along one of the compartments and transferred at the end of that compartment to the other compartment and passed along in the opposite direction in the other compartment.
U.S. Pat. No. 2,861,688 to Harms discloses a relatively complicated device for separating small cuttings and other particulate material from fluids. The device is designed for separating mixtures consisting of particles having a density less than the density of the fluid and particles having a density greater than the density of the fluid. The particles having a density less than the fluid are separated prior to removing the denser particles to decrease the settling time. The device has two conveyor systems, an upper one and a lower one. The upper conveyor system separates the less dense material from the tank, and has a horizontal screen associated therewith through which finer particles of greater density fall to be separated from the tank by the lower conveyor system. The main problem with this device is that the horizontally disposed screen becomes blocked very easily, making the device unsuitable for use with the dense sludges obtained during earth drilling operations.
U.S. Pat. No. 2,588,233 to Hapman discloses a device for removing sediment from fluids. The device is provided with a V-shaped floor, to reduce the overall space occupied by the device, and to enhance settling of material from the fluid. The device does not have a separation screen but is provided with a series of baffles which are arranged to cause the fluid to pass through a circuitous path. Mention is made in the patent of the possibility of providing conventional screens if additional removal of material is required, but there is no specific description of the type of screen to be used and no indication of where the screen should be placed in the device.
It can be appreciated, therefore, that a need exists for an improved device for separating rocks, clay and other chunks of agglomerated material suspended in earth drilling fluids which does not suffer from the blocking problems associated with prior devices. In particular, a need exists for a device which effects substantially complete separation of such material from the drilling fluid in a relatively short period of time with little or no stoppage to unblock the device.